It has been realized for many years that the efficiency of heat exchangers has consistently decreased with use, particularly with hard water or other such fluids as the heat-transfer medium, as films or scales develop upon the heat transfer surface. Thus, particularly in tubular heat exchangers which include a series of tubes, and a heat-exchange medium is carried either between or through these tubes for heat transfer with a second heat-transfer medium through the tubes thereof, as such films or scales begin to develop on the surface of or within the tubes, the rate of heat transfer cannot be maintained without intermittantly shutting down the system and scraping or otherwise cleaning these tube surfaces.
Many systems have been suggested for continuously operating such heat exchangers, and particularly wherein discrete particles or cleaning bodies are maintained in the flow of either of the media, i.e. either through the tubes themselves or between the tubes. Thus, U.S. Pat. No. 3,021,117 to Taprogge discloses a self-cleaning heat-exchanger which employs rubbing bodies, such as sponge rubber particles in a continuous loop passing through the individual tubes 19 of the heat exchanger in order to continuously contact the surface thereof and maintain same free from particulate buildup. In order to recirculate same, however, the patent teaches the use of a device for intercepting and conducting the rubbing bodies to a return device, comprising a funnel-shaped strainer 23 or other screen or grating, which permits the water removed from the discharge end of the heat-exchanger to pass onward but collects the rubbing bodies for return back to the inlet end of the heat exchanger. This device thus requires that the funnel or strainer 23 directly intercept the swiftly moving rubbing bodies, which thus impinge directly on the surface thereof. For this reason the use of more substantial rubbing bodies, such as steel balls, would not be practicable in this invention since damage would occur to the screen 23 during use.
Another such system for continuously cleaning the tube surfaces of tubular heat exchangers is disclosed by Treplin in U.S. Pat. No. 3,219,195. In this apparatus, the cleaning bodies 5, which are preferably elastic in character and have the specific weight of the cooling water, are recirculated by their collection from the water discharged from the heat exchanger in sieve 6a and 6b, and then directed into a sluice 9 provided with a sieve basket 10. These bodies are thus permitted to enter the sluice 9 through line 8, which passes through sieve basket 10, when valve 12 is open, and subsequently these cleaning bodies are permitted to re-enter the fluid stream through line 16, which enters sluice 9 through sieve basket 10, when valve 13 is opened. The continuous opening and closing of valves 12 and 13 is therefore required in this device, and again the cleaning bodies impinge directly upon a screen or sieve 6a and 6b for collection as the water passes therethrough.
Yet another such device is taught in U.S. Pat. No. 1,795,358 to Schmidt, which employs small hard objects, such as balls, for passage through the heat exchanger tubes. While the use of such hard objects is particularly helpful in preventing the buildup of foreign material on the surface of such heat exchange tubes, several additional difficulties are prevented therewith. Thus, this patent requires the use of a suitable screen 24 again to intercept the balls 37 passing from the outlet side of the heat exchanger for return, and additionally the balls 37 must pass through the pump 31 for re-introduction back to the inlet side of the heat exchanger. Considerable damage is thus caused to the pump after continuous use with these hard metal objects therein.
It is therefore apparent that in each of these systems the cleaning bodies are collected for re-circulation by impinging directly upon a screen or sieve, which is therefore subject to damage, particularly when harder objects such as steel balls are employed. Furthermore, each of these prior art techniques require that the cleaning bodies pass through a pump for re-circulating same, therefore subjecting that pump to considerable damage and necessary replacement.
It is therefore an object of the present invention to provide an apparatus which is capable of overcoming each of these difficulties encountered in these devices of the prior art.